In recent years, as residential photovoltaic power generation devices, fuel cells, power storage devices and the like become widespread, various circuits have been proposed and provided as power conversion devices that convert the output of DC power sources to AC power. For example, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2014-64431) discloses a power conversion device (in Patent Document 1, a “multi-level power conversion device”) that generates an AC output converted to a plurality of voltage levels (output levels) from a DC voltage source.
The power conversion device described in Patent Document 1 is a 5-level inverter that outputs voltages of 5 levels. The power conversion device includes two DC capacitors, two flying capacitors and sixteen switching elements. In this power conversion device, in a state in which a DC voltage E is applied to a series circuit of two DC capacitors, the respective switching elements are controlled so that the voltage across each DC capacitor becomes E/2 and the voltage across each flying capacitor becomes E/4, thereby outputting voltages of five levels.
However, in the above-described conventional example, a problem is posed in that the common mode (in-phase) voltage fluctuates when changing the output voltage. For this reason, in the above-described conventional example, there is a possibility that due to the fluctuation of the common mode voltage, a noise is generated or a leakage current flows.